Removing Pointing Stains

[John17]

Has anyone got any tips for removing the staining that some times occurs when pointing and laying slabs?

[alan ditchfield]

This depends on these three things; what sort of mortar what sort of flags and how long have the stains been left on the flags for. Alan

[84-1093879891]

There's some basic tips on the Dealing with Stains page.

Don't use any acid-based cleaner with imported sandstones.

[mouldmaker]

I'd like to throw my tuppenceworth into the ring by advising against using acid cleaners on precast concrete paving. The tips offered on the 'Dealing with Stains' pages are fine, but I cannot emphasise enough the pre-wetting, followed by application of acid. Don't allow thw acid to penetrate; better several applications than disaster.

Overapplication of acid may cause discoloration, and a visible degradation of the face. It can also damage resistance to frost and make them prone to dusting. My advice would be, unless the staining is minimal and easily removed, replace the affected slabs.